It has long been the practice to apply overseals of one kind or another with special hand and power tools which were able to crimp a metal portion of the overseal tightly around an upstanding opening neck designed to receive the seal. The application step itself is quite labour intensive and relatively inefficient. Consequently a number of hand applied overseals or closure caps have come forth which to a certain degree obviate the above-mentioned application tools. Our prior patent specifications WO2005/056411, WO2005/056412 and WO2008/139196 concern closure caps intended for application by hand, without the aid of special tools. To be effective such closure caps or overseals need to meet a number of rather demanding criteria. Obviously the hand application has to be simple and relatively effortless to satisfy normal filling line speeds. Once the drum or other container is shipped, of paramount importance is the ability of the cap or overseal to guard against unauthorized access to the drum contents. This means that ideally the cap or overseal cannot be physically removed without destroying it or making unauthorized access clearly noticeable such that the cap or overseal cannot be reapplied in unaltered form to the drum closure.
The caps or overseals must be of sufficiently robust construction so that they (and in particular their tamper indicating features) are not destroyed by the normal handling of the shipping containers or drums to which they are attached. Tamper indicating features which are destroyed or damaged in this way will give a false positive tamper indication. A performance criterion also of major importance is the ease with which the cap or overseal can be removed from the underlying container (e.g. drum) closure in an authorised manner such that subsequent replacement of the overseal is not possible. As this requires destruction of the cap or overseal in some fashion to prevent reuse this therefore to some extent conflicts with the requirement for robustness. In this regard the use of sharp cutting or puncturing implements is undesirable due to the likelihood injury or of accidental damage to the underlying closure. Thus, in addition to the overseal's robust construction, hand removability is yet another advantageous attribute.
WO2005/056411 and WO2008/139196 disclose closure caps intended for use together with specially modified complementary plastics closure plugs or bungs for shipping containers. The closure caps concerned have attachment portions which engage with an undercut groove formed in specially modified wrench-engaging lugs integrally moulded in the plug. WO2005/056412 discloses a closure cap which is suitable for application to the neck of a filling opening formed in metal, of the kind commonly found in metal shipping containers such as metal drums. As such it may therefore be used for tamper indicative protection of either plastics or metal closure plugs installed in such metal drums.
It is known to apply sealing foils to drum closure plugs, as disclosed in Indian patent application nos. 0814CHE2010 and 2809CHE2009. However according to those disclosures the foil application step takes place on the filling line, after the containers are filled and closed. The foil application step is a relatively slow process unsuited to automated filling lines. Checking for and remedying defective foils may also be problematic.